Objectives To compare the prevalence of use of potentially inappropriate medicines (PIMs) between older patients living in their own homes versus those living in nursing or residential homes, and to test the association between exposure to PIMs and mortality.

Design Cohort study stratified by place of residence.

Setting Tayside, Scotland.

Participants All people aged between 66 and 99 years who were resident or died in Tayside from 2005 to 2006.

Main outcome measures The exposure variable was PIM use as defined by Beers' Criteria. All cause mortality was the main outcome measure.

Results 70 299 people were enrolled in the cohort of whom 96% were exposed to any medicine and 31% received a PIM. Place of residence was not associated with overall risk of receiving PIMs, adjusted OR 0.94, 95% CI 0.87 to 1.01. Exposure to five of the PIMs (including long-acting benzodiazepines) was significantly higher in nursing homes whereas exposure to five other PIMs (including amitriptyline and NSAIDs) was significantly lower. Exposure to PIMs was similar (20–46%) across all 71 general practices in Tayside and was not associated with increased risk of mortality after adjustment for age, gender and polypharmacy (adjusted OR 0.98, 95% CI 0.92 to 1.05).

Conclusions The authors question the validity of the full list of PIMs as an indicator of safety of medicines in older people because one-third of the population is exposed with little practice variation and no significant impact on mortality. Future studies should focus on management of a shorter list of genuinely high-risk medicines.